The Environmental Protection Agency plans to try to remove radioactive waste from a Missouri dump as part of a widespread effort to speed up how the government deals with the country's most toxic sites.

The move, which is among the agency's most urgent priorities, would end years of dispute over how to deal with thousands of tons of factory waste from the nuclear-weapons program buried for decades at West Lake landfill near St. Louis. Under the agency's proposal, an excavation will remove most of the dump's radioactivity and a permanent cap would be installed over the rest. It would take five years and cost $236 million, according to an announcement Thursday from the EPA.

West Lake is one of more than 1,300 sites in the Superfund program, which manages places highly contaminated by lead, asbestos, radiation and other pollutants that can cause cancer, birth defects and other health and environmental harms. EPA Administrator Scott Pruitt has promised to put renewed attention on resolving these threats, some of which have lingered for decades. He said the West Lake decision demonstrates his vision for the program.

"This sends a message that we're actually going to get results," Mr. Pruitt said in an interview with The Wall Street Journal. "Frankly it's just what we ought to be doing."

Major progress on that work could become a legacy-shifting achievement for a regulator now known largely for making friendlier relationships with industry and dismantling programs from the previous administration under President Barack Obama. President Donald Trump has pushed to rollback Obama-era rules designed to fight climate change and water pollution, among others, to help the energy industry and other businesses.

Mr. Pruitt has also argued the EPA could be more productive by focusing more on longstanding programs and problems, especially superfund cleanups.

The EPA first listed West Lake in 1990, but has been unable to come to a solution for the site. It decided in 2008 to leave the waste in place and cover it with a protective cap. But local residents protested, demanding the waste be hauled away and leading the EPA to reassess its plan. Some also accused the agency of pressuring an independent review board to soften challenges of an EPA plan.

West Lake's owner, Republic Services Inc., along with Exelon Corp. and the Energy Department are responsible for the cost, though their shares have yet to be determined, the agency said. A Republic subsidiary involved with the site said it "is pleased that the EPA has finally ended decades of study and again is issuing a proposed plan for the site." It said it plans to work with the EPA, but that it could be years before the proposal gets finalized and the cleanup starts. Exelon and the Energy Department didn't immediately respond to requests for comment.

The agency's proposal suggests the best options are to put the excavated waste into a cell on site or ship it away to another site, Mr. Pruitt said. An off-site solution would be out of state. Mr. Pruitt noted another site about 20 miles away where similar waste is encased in a steel and concrete cell that can safely hold the waste for 1,000 years. The agency will be taking public comments on the proposal for up to three months and will consider those comments in deciding where the waste ultimately goes.

That plan is "a lot better" than what the EPA proposed in 2008, but it still isn't satisfying to the locals whose protests helped scuttle the proposal back then, according to Ed Smith, policy director at Missouri Coalition for the Environment, based in St. Louis. Locals have long asked for all the material to be taken away, saying the site is in too populated an area with earthquake risks.

"It's not enough," Mr. Smith said. "This is not the type of place you want to keep this long term."

The EPA and Republic have said their radiation sampling hasn't shown evidence of the site posing a threat to the public. But one study has shown waste likely has migrated off-site and smoldering garbage buried in another part of the landfill may be also threatening to heat the radioactive waste. The Journal wrote about the West Lake controversy as part of a 2013 series on the legacy of the nuclear-weapons program.

"The EPA has lost credibility within the community, and left parents living in fear for their children's health and safety," Missouri Republican Sen. Roy Blunt had said during a 2016 effort to strip the agency of its oversight.

To help improve the Superfund program, Mr. Pruitt created a new list of sites in December -- even though the program already had a priorities list -- to highlight 21 sites in need of "immediate and intense attention." That list includes West Lake. While critics have called the move political posturing, Mr. Pruitt has framed it as a way to renew emphasis and urgency on the program.

He has repeatedly listed Superfund sites as a priority, especially in 2018. He told the Journal his goal is for the agency to come to decisions on nearly 30 sites this year.

But Mr. Pruitt is likely to run into many of the same problems his predecessors have encountered trying, and often struggling, to run the Superfund program, said Nancy Loeb, director of the Environmental Advocacy Center at Northwestern University. That includes shrinking budgets and negotiations with companies that often lead to compromise cleanup plans, she added. The fact that EPA opted for a solution that didn't provide the maximum amount of protection in the West Lake case, and that will still take five years once the project starts, are troubling signs for the progress Mr. Pruitt wants to make, she said.

"That doesn't sound like we're doing a lot very quickly," Ms. Loeb added. "I'm always glad to see some things happening, but there was nothing especially convincing about today's announcement, for this site, or more broadly how this administration is going to move."